Three multiply charged primary cosmic ray interactions with carbon nuclei are reported, in which the number of materialized electron pairs within a distance of about 0.3 conversion length is larger than predicted from isospin considerations. These are the most energetic (sigma E gamma  4 TeV) of the low multiplicity ( 15 tracks) events observed in the Japanese-American Cooperative Experiment (JACEE-2) emulsion chamber

Burnett, T. H.

Dake, S.

Fuki, M.

Gregory, J. C.

Hayashi, T.

Holynski, R.

Iwai, J.

Jones, W. V.

Jurak, A.

Lord, J. J.

English

NASA Technical Reports Server

172 HE 1.4-6
EXCESSIVE PRODUCTION OF ELECTRON PAIRS
BY SOFT PHOTONS IN LOW MULTIPLICITY ION INTERACTIONS*
The JACEE Collaborationt
T. H. Burnett h, S. _ake b, M. _uki d, J. C. Gregory g,
•g .i .n e i
T. Hayas_i , R. Holynskl , J. Iwal , W. V. Jones _^A. Jurak ,
J. J. Lor_, O. Miyamu_a c, T. OgataC,fT. A. ParnellT, T. Saito a,
S. Strausz , T. _abuki , Y. Tak_hashi , T. _ominaga c, J. Watts g,
B. Wilczynska ±, R. J. Wilkes n, W. Wolter I, and B. Wosiek I
a Institute for Cosmic Ray REsearch, University of Tokyo;
Department of Physics, Kobe University;
c Departmen_ of Applied Mathematics, Osaka University;
Okayama University of Science;
e Department of Physics and Astronomy, Louisiana State University;
f Space Science Laboratory, NASA Marshall Space Flight Center;
g _epartment of Chemistry, University of Alabama, Huntsville;
Visual _echniques Laboratory, University of Washington;
i Institute for Nuclear Physics, Krakow.
Abstract
We report here on three multiply charged primary
cosmic ray interactions with carbon nuclei, in which the
number of materialized electron pairs within a distance
of about 0.3 conversion length is larger than predicted
from isospin considerations. These are the most
energetic (Z E > 4 TeV) of the low multiplicity (< 15
tracks) events_observed in the JACEE-2 emulsion chamber.
1. Introduction.
The Japanese-American Cooperative Emulsion Experiment (JACEE)
employs balloon-borne emulsion chambers to study the energy spectra,
charge composition, and nuclear interactions of ultrahigh energy cosmic
rays. Following exposure and processing, the emulsion plates are
distributed to the participating laboratories for detailed scanning,
tracing, and subsequent measurements using optical microscopes.
Preliminary analysis is carried out on the data collected in the
individual laboratories before it is combined with data from the other
laboratories in the JACEE data bank. Comparisons among the datasets
from the various laboratories are used to control the overall quality of
the data.
The data presented herein were collected in the plates of the
JACEE-2(second in the JACEE series of annual balloon flights) emulsion
chamber. , The unusual nature of the
events was discovered during a study of the techniques used for
determining the transverse momenta of high energy gamma rays emanating
from a primary vertex in the target section of the emulsion chamber.
https://ntrs.nasa.gov/search.jsp?R=19850027581 2020-03-20T17:21:18+00:00Z
HEI.4-6
173
The JACEE-2 chamber consisted of a target section upstream of a
thin calorimeter, which was used to measure the energies of cascades
initiated by energetic gamma rays. The target was comprised of
approximately 50 layers of double-sided emulsion plates (50 micron
emulsion films on both sides of an 800 micron acrylic base plate)
interleaved with 2 mm thick acrylic sheets. The calorimeter, which was
a multilayer sandwich of lead sheets, x-ray films, and emulsion plates,
had a vertical thickness of about 7 c.1.
Except for high multiplicity events, individual tracks of hadrons
and leptons can be resolved near the vertex and then followed plate-to-
plate to the calorimeter section. Consequently, cascades developing in
the calorimeter can be correlated with tracks from the vertex.
2. Results.
The cones defined by the tracks of energetic charged particles from
low multiplicity (< 15 tracks) interactions were scanned for possible
evidence that cascading had begun in the target section of the emulsion
chamber, i.e., upstream of the calorimeter. In this report we discuss
the observations on the three most energetic (EEy > 4 TeV) events in the
sample. Using standard nomenclature the three events are of the types:
+
He + C + 2p + 9_- ++2Y Event F0358
N + C + 3a + p ++87- + 3Y Event F0312
He + C + 2p + 8_- + 4y Event F0214
where C represents the material of the acrylic target plates.
The detailed characteristics of the events are presented in
Table 1. A total of 9 electron pairs were found near the interaction
vertices. This is more than twice the number expected from photon
conversions, assuming that the number of emitted photons in the volume
scanned for pairs is equal to the number of charged pions emitted in
that volume •
The pseudo-rapidity distributions of the produced hadrons in the
forward cone are given in Fig. l, which also shows the pseudo-rapidities
of proton fragments, p, from the interactions and the photons, Y,
producing the observed electron pairs. Proton fragments from the
p lr pg"
F0358 *-I T I] I ta I II
,,_,_ p
F0312 -'-'Hll I f I _ 1(i i I I .
r _ pr p f
,, F0214 _ , _ , IT I , II II ,!1 _ , li , , __
-11.0 -10.0 -9.0 -8D -7.0 -6.0 -5.0
]n tg 8/2
Fig. i. Pseudo-rapidity distributions of produced
particles, proton fragments, and gamma rays.
HEI.4-6
174
projectile were assumed to have the smallest emission angles among the
charged particle tracks.
Figure 2 Shows the dependence of the number of photons converted
into electron pairs as a function of distance z from the interaction
vertex. The solid line represents the number of materialized gamma
rays, N , producing electron pairs inside the scanned volume while the
dashed line shows the number of pairs expected in that volume from
i sos pin cons ide rat ions.
" 7Y
I
I I I I
0 01 02 O3 O4 O_
z [c.l.]
Fig. 2. Number of gamma rays producing electron pairs
as a function of distance from the vertex.
3. Discussion.
The largest excess of pairs was observed in the most energetic
event (E ~ 60 TeV), in which 4 photons materialized within a distance
of 0.i c?l. Three of the pairs were found in a very narrow cone of
0.0001 radians. The pairs evolved to 18 electrons in a distance of
0.4 c.1. and to 30 electrons in 0.5 c.l. A comparison with the results
of cascade theory (Table i, Col. 6) indicates that the materialization
of one photon in the vicinity of the vertex is unlikely to produce the
fast developing cascade. The observed pairs are most likely first
generation and not fluctuations in the cascade development.
A characteristic feature of all the observed pairs is their narrow
collimation, which suggests that the_were emitted by the fragmenting
projectile. Internal bremsstrahlung ' from the deceleration of charged
particles (or quarks) may e_plain the observed excess of pairs, since at
projectile energies E > lO± eV the Doppler shift could raise the energy
of soft photons above the _0.5 GeV detection threshold. At the present
stage, however, fluctuations in production of pairs can not be ruled
out, and larger statistics are needed to give a quantitative description
of these anomalous pairs.
HE 1.4-6
175
Table I. Characteristics of the interactions.
Event Eo(TeV) Pair z(c.l.) ne ne+ ne*
F0358 24.0 l 0.04
2 0.2B 4 2.1
F0312 24.6 I 0.05
2 0.24 4 1.2
F0214 60.0 i 0.01 2
2 0.02 4
3 0.06 6
4 0.08 8 i.l
........036 ...........
0.55 30 6
0.73 30 9
Table Captions
Eo - primary energy estimated from the neutral component (ZE) and
inelasticity coefficient k = 0.5 .... Y
,J
z - distance to point of conversion (in conversion units).
ne - number of electrons at given z.
+
ne - number of electrons predicted from the probability of pair
conversion, based on isospin considerations.
ne* - number of cascade theory electrons with energie_w > 0.5 GeV
produced by an electron pair of energy Wo = 5 TeV _j. The cascade
energy Wo is estimated from the longitudinal development of the
cascade downstream in the calorimeter.
References
* Research supported in part in the USA by DOE, NASA, and NSF and in
part in Japan by JSPS and ICR.
T Mailing address for this paper: Institute for Nuclear Physics, ul.
Kawiory 26A, 30-055, Krakow, Poland or Department of Physics and
Astronomy, Louisiana State University, Baton Rouge, LA ?_803, USA.
i) Janossy, L. and Messel, H., (1951) Proc. Royal Irish Acad. 54(A), 217.
2) BJorken, J. D. and McLerran, L., (1983) Fermilab-Pub-84/BS-T.


Excessive production of electron pairs by soft photons in low multiplicity ion interactions

Excessive production of electron pairs by soft photons in low multiplicity ion interactions

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